(1) Field of the Invention
The present invention relates to display panel apparatuses and methods of fabricating the display panel apparatuses, and particularly relates to an organic electroluminescent (EL) display panel apparatus using organic luminescent material.
(2) Description of the Related Art
The organic EL display apparatus is a light-emitting display apparatus using electroluminescence of organic compounds, and has been in practical use as a small display apparatus used for mobile phones and others.
The organic EL display apparatus is configured by organic EL devices arranged on a substrate. The organic EL devices can be individually controlled per pixel for light-emission. A typical organic EL display apparatus is manufactured by stacking a driving circuit, an anode, an organic layer, and a cathode on a substrate. The organic layer includes, in addition to an organic EL layer made of an organic compound, at least one of functional layers such as a hole transport layer and an electron transport layer. With this configuration, charge is injected to the organic EL layer from the anode or the cathode through the hole transport layer and others, and the injected charge is recombined in the organic EL layer, and the organic EL layer emits light.
It is important that the operational current sufficient for the organic EL display device in each pixel is supplied in order to obtain good display quality in the organic EL display apparatus. This is because lack of sufficient operational current supply decreases luminance, causes uneven luminance, and reduction in contrast, which are causes for degraded display quality.
Conventionally, in order to achieve good display quality, a configuration for supplying sufficient operational current to the organic EL device in each pixel of the organic EL display apparatus has been proposed (for example, see Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2005-242383).
The light-emitting apparatus according to Patent Literature 1 includes a cathode-line connected to the cathode, which is provided outside of the effective region in which pixels each including a light-emitting device (referred to as display section in this Specification) is provided to surround the effective region, and the power supply line connected to the pixel electrodes is provided between the cathode-line and the effective region.
According to the light-emitting apparatus with the configuration described above, it is possible to secure sufficient contact area for the cathode-line and the cathode, while suppressing the electric resistance between them to minimum. Accordingly, it is possible to prevent the reduction in the amount of current supplied to the light-emitting device by a voltage drop due to the electric resistance.
In terms of the viewpoint for supplying the sufficient operational current to the organic EL device, larger area of the cathode-line in the light-emitting apparatus according to the conventional technology is preferable. However, providing the cathode-line in a wide area surrounding the display section raises the following problems with the conventional technology.
More specifically, in the fabrication process of the display apparatus, the lower electrode separated for each pixel is generally formed by photo etching after forming the planarizing film is formed, and the organic layer is subsequently stacked. When forming the planarizing film and the lower electrode, due to cleaning water and chemical solutions such as develop solution and acid, moisture, acid, and other components are absorbed by the planarizing film. Accordingly, if the planarizing film with the moisture and acid absorbed is covered by an electrode plate used for the cathode-line, for example, the planarizing film is sealed with the moisture and acid absorbed inside.
If the organic layer is stacked above the planarizing film in this state, the components such as moisture and acid included in the planarizing film may leak to the organic layer. As a result, the quality of the organic layer is degraded due to the reaction of the organic layer with the components such as moisture, acid, and others, causing a problem of shrinking pixels. In particular, when Balium (hereafter referred to as Ba) is included in the organic layer, Ba reacts to the moisture, shrinking the pixels.
Furthermore, due to gas components such as moisture and acid sealed in the planarizing film, the electrode plate is peeled off by the pressure of the gas component, leaking components such as moisture and acid to the organic layer at the peripheral portion of the display section. As a result, there is a problem that the organic layer at the peripheral portion of the display section reacts with the components such as moisture and acid, changing the injection property of the organic layer. As a result, this causes a problem of uneven display at the peripheral portion. In particular, when Ba is included in the organic layer, Ba in the organic layer reacts with moisture, turning the peripheral portion white.
Patent Literature 1 fails to suggest an effective solution for overcoming these problems concerned in a case where the electrode plate used as the cathode-line is provided, and the planarizing film covers a wide region surrounding the display section.